It is known in the packaging industry to provide dispensing devices that dispense liquid adhesive on packaging materials in spots or any other desired pattern, such as a swirl, a spray, a plurality of beads, drops or droplets. The packaging material is then folded in a predetermined manner so that the dispensed adhesive comes in contact with mating potions of the packaging material to form the desired container or package. These dispensing device are also employed to dispense adhesives on substrates, woven and non-woven, materials and products assemblies. Due to high speed nature of this assembly process, dispensing devices have been developed using electrical control systems which are also known as gun drivers.
Known dispensing devices include a valve-type system containing a plunger (also known as an armature or valve needle) received within an orifice, wherein a solenoid is employed to control the movement of the plunger from a closed position to a dispensing position and back again to a closed position, such as set forth in U.S. Pat. No. 5,375,738, the disclosure thereof is incorporated herein by reference, and which is owned by the assignee of this invention.
Gun drivers have been developed employing electric circuit controls to enhance the operation of the dispensing device. Many factors contribute to the efficient operation of such a dispensing device including, but not limited to, the viscosity of the adhesive to be applied, the heat generated by the resistance and inductance of the solenoid, the temperature of the fluid or adhesive to be applied, the desired pattern of the adhesive and the number of solenoids connected to the control device. To insure the proper operation of the dispensing device or devices, it is important that the plunger quickly open and quickly close the orifice when desired. To achieve this, it is required that the solenoid receive a fast pull-in current that quickly opens the plunger from the orifice at the beginning of the dispensing cycle, a minimal holding current which holds the plunger in an open position while minimizing the amount of heat buildup in the solenoid coil during dispensing, and a fast dissipation of current from the solenoid coil so that the plunger is quickly closed upon the orifice at the end of the dispensing cycle. U.S. Pat. No. 4,453,652, which is assigned to the assignee of this invention, describes a method of reducing the current flow through a coil once the plunger has moved to its open position.
It is presently known to supply current to multiple dispensing modules from a single current source. In order to properly control the operation of these multiple dispensing modules, it is required that an operator place switches in predetermined positions or insert or remove physical jumper connections between the solenoids so that they operate in the desired sequence. Several problems arise when the aforementioned switches or physical jumper connections are not properly implemented. For example, if not enough current is supplied to the solenoids, the required pull-in current value may not be attained so that the solenoids remain closed or are delayed in their opening. As such, the desired dispensing pattern is not obtained. It is also possible that too much current could be supplied to a solenoid so that the solenoid or plunger assembly itself is damaged, thereby causing downtime to the manufacturing process as the solenoid or dispensing device is replaced It will also be appreciated that current dispensing devices do not allow for the easy determination of whether a solenoid is operating within a predetermined current range. In other words, if after a period of time the inductor contained within the solenoid begins to degrade, there is no facile means for quickly correcting the problem.
Based upon the foregoing, it is apparent that there is a need for a device to identify the number of inductive loads or solenoids connected in parallel to a gun driver to assure that an appropriate level of current to the solenoids is attained. Moreover, there is a need in the art for a monitoring device to determine if any one of the solenoids connected to a dispensing device is operating with an unacceptable current level.